Solved the problem the tried-and-true way: bought a cheap nVidia card. It's a piece of crap, but it worked immediately.
This is far from my first ATI card in Linux: each time I managed eventually to get it to work, so I'm really sorry to have to give up, but I'd wasted a month of aggravation on this thing, with no way to see inside to figure out what to try next.
More than a month, actually, so I couldn't return the card. Maybe I'll send it as a Christmas gift to Hector Ruiz. Or keep it in mothballs till RadeonHD drivers can do 3D acceleration.
So what was your problem ?
Not able to get 3d working on your card?
On my 2600pro(working 2d and 3d cat 7.11) i got this
(**) fglrx(0): Textured Video is enabled.
(II) LoadModule: "glesx"
(II) Loading /usr/lib/xorg/modules//glesx.so
(II) Module glesx: vendor="X.Org Foundation"
compiled for 7.1.0, module version = 1.0.0
ABI class: X.Org Server Extension, version 0.3
(II) Loading extension GLESX
(II) fglrx(0): GLESX enableFlags = 26
(II) fglrx(0): Using XFree86 Acceleration Architecture (XAA)
Screen to screen bit blits
Solid filled rectangles
Solid Horizontal and Vertical Lines
Driver provided ScreenToScreenBitBlt replacement
Driver provided FillSolidRects replacement
(II) fglrx(0): GLESX is enabled
(II) fglrx(0): X context handle = 0x1
(II) fglrx(0): [DRI] installation complete
(II) fglrx(0): Direct rendering enabled